Draw the outline, adding in some folds at the bottom which should hang pretty straight (but not perfectly straight because that would look awkward). I want the material to look thin so I've followed the outline of the base pretty closely.
Fill in the outline and start shading - this step is really more so you have an idea of where the shading will go, so don't worry about making the folds and creases too dark, we'll blend them in as we go along. Making the folds and creases long and thin gives the impression of thin fabric.
And start blending. Lengthen the shading and colour over the bits that are too dark.
I want it to look a bit softer so I either needed another shade or to re-jig the palette. Unsurprisingly, I took the lazy option.
I used a colour slightly lighter than the outline to blend the folds a bit better - it's also a good idea to add a little dithering (or another shade) for the skirt folds where needed, especially if you're using a bigger base.
Add some highlights. I re-jigged the palette again to lower the contrast. The shading will tell you where to put highlights - you might need to colour over the shading again if it looks too severe against the highlights.
Add lighter highlights. Best not to go overboard with this shade and only add it where there are big patches of light (like on the bigger folds of the skirt) or where you want the creases to look sharp (like across her stomach).
I've shaded the outline because I think it looks more 'finished', but there's nothing wrong with leaving the outline dark if that's the look you're going for.
Don't forget to shade the base under the dress!
